In projection televisions or projection screens for projectors, which are a combination of a Fresnel lens and lenticular lenses, a moire pattern that is produced due to a group of concentric circles on the Fresnel lens and a group of parallel straight lines of the lenticular lenses is known to be either elliptical or hyperbolic depending on the pitch ratio between these two groups (see U.S. Pat. No. 2,567,654). FIG. 6 is a view showing one example of the moire pattern in the shape of an ellipse (hereinafter also referred to simply as "elliptical moire"); and FIG. 7 is a view showing one example of the moire pattern in the shape of a hyperbola (hereinafter also referred to simply as "hyperbolic moire"). In FIG. 6, the elliptical moire is such that its focal point corresponds to the center of the Fresnel lens. Further, in FIG. 7, the asymptotic lines of the hyperbolic moire are those two lines that cross each other at the center of the Fresnel lens. It is noted that the angle formed with these asymptotic lines varies depending on the pitch ratio between the lenticular lenses and the Fresnel lens.
In many cases, perceived by an observer is generally either one of the moire patterns of these two types. In practice, however, the moire patterns of these two types are simultaneously produced. When the pitch ratio between the lenticular lenses and the Fresnel lens is n+0.5 (n: integer), the intensities of the moire patterns of the two types become lowest, and the cycles (pitches) of these moire patterns become identical (see Japanese Patent Laid-Open Publication No. 52985/1981). Even if the pitch ratio between the lenticular lenses and the Fresnel lens only slightly deviates from n+0.5, the cycles (pitches) of the two moire patterns do not agree with each other, and a secondary moire pattern is produced by the moire patterns of these two types. This secondary moire pattern is scalelike, and produced on the transverse axis of the lenticular lenses in the repeating direction.
This secondary moire pattern is minimized when the pitch ratio between the lenticular lenses and the Fresnel lens is in the vicinity of n+0.4, or of n+0.6 (see Japanese Patent Publications No. 68365/1991 and No. 72972/1991). However, when the pitch ratio between the lenticular lenses and the Fresnel lens is in the vicinity of n+0.4, or of n+0.6, the intensity of the primary moire pattern (elliptical moire or hyperbolic moire) will not become so low. In the conventional projection screens, the pitch of the lenticular lenses is approximately 0.7 to 1.0 mm, and that of the Fresnel lens is approximately 0.1 to 0.15 mm, so that the pitch of the primary moire pattern (elliptical moire or hyperbolic moire) which varies relative to the pitch of the lenticular lenses becomes relatively large. For this reason, the conventional projection screens have such a problem that the primary moire pattern (elliptical moire or hyperbolic moire) tends to become conspicuous due to the size of its pitch.